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Message-ID: <CAJ8uoz3Cc4dN_dfh5UFHPDEEVMLWg_o3Mi0PRMJOqfhRER2DLg@mail.gmail.com>
Date: Wed, 29 Jul 2020 15:22:36 +0200
From: Magnus Karlsson <magnus.karlsson@...il.com>
To: Maxim Mikityanskiy <maximmi@...lanox.com>
Cc: Magnus Karlsson <magnus.karlsson@...el.com>,
Björn Töpel <bjorn.topel@...el.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Network Development <netdev@...r.kernel.org>,
Jonathan Lemon <jonathan.lemon@...il.com>,
bpf <bpf@...r.kernel.org>, jeffrey.t.kirsher@...el.com,
anthony.l.nguyen@...el.com,
"Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>,
Maciej Fijalkowski <maciejromanfijalkowski@...il.com>,
cristian.dumitrescu@...el.com
Subject: Re: [PATCH bpf-next v4 08/14] xsk: enable sharing of dma mappings
On Tue, Jul 28, 2020 at 11:00 AM Maxim Mikityanskiy
<maximmi@...lanox.com> wrote:
>
> On 2020-07-21 08:04, Magnus Karlsson wrote:
> > Enable the sharing of dma mappings by moving them out from the buffer
> > pool. Instead we put each dma mapped umem region in a list in the umem
> > structure. If dma has already been mapped for this umem and device, it
> > is not mapped again and the existing dma mappings are reused.
> >
> > Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> > ---
> > include/net/xdp_sock.h | 1 +
> > include/net/xsk_buff_pool.h | 7 +++
> > net/xdp/xdp_umem.c | 1 +
> > net/xdp/xsk_buff_pool.c | 112 ++++++++++++++++++++++++++++++++++++--------
> > 4 files changed, 102 insertions(+), 19 deletions(-)
> >
> > diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> > index 126d243..282aeba 100644
> > --- a/include/net/xdp_sock.h
> > +++ b/include/net/xdp_sock.h
> > @@ -30,6 +30,7 @@ struct xdp_umem {
> > u8 flags;
> > int id;
> > bool zc;
> > + struct list_head xsk_dma_list;
> > };
> >
> > struct xsk_map {
> > diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h
> > index 83f100c..8f1dc4c 100644
> > --- a/include/net/xsk_buff_pool.h
> > +++ b/include/net/xsk_buff_pool.h
> > @@ -28,6 +28,13 @@ struct xdp_buff_xsk {
> > struct list_head free_list_node;
> > };
> >
> > +struct xsk_dma_map {
> > + dma_addr_t *dma_pages;
> > + struct net_device *dev;
> > + refcount_t users;
> > + struct list_head list; /* Protected by the RTNL_LOCK */
> > +};
> > +
> > struct xsk_buff_pool {
> > struct xsk_queue *fq;
> > struct xsk_queue *cq;
> > diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
> > index 372998d..cf27249 100644
> > --- a/net/xdp/xdp_umem.c
> > +++ b/net/xdp/xdp_umem.c
> > @@ -199,6 +199,7 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
> > umem->user = NULL;
> > umem->flags = mr->flags;
> >
> > + INIT_LIST_HEAD(&umem->xsk_dma_list);
> > refcount_set(&umem->users, 1);
> >
> > err = xdp_umem_account_pages(umem);
> > diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
> > index c563874..ca74a3e 100644
> > --- a/net/xdp/xsk_buff_pool.c
> > +++ b/net/xdp/xsk_buff_pool.c
> > @@ -104,6 +104,25 @@ void xp_set_rxq_info(struct xsk_buff_pool *pool, struct xdp_rxq_info *rxq)
> > }
> > EXPORT_SYMBOL(xp_set_rxq_info);
> >
> > +static void xp_disable_drv_zc(struct xsk_buff_pool *pool)
> > +{
> > + struct netdev_bpf bpf;
> > + int err;
> > +
> > + ASSERT_RTNL();
> > +
> > + if (pool->umem->zc) {
> > + bpf.command = XDP_SETUP_XSK_POOL;
> > + bpf.xsk.pool = NULL;
> > + bpf.xsk.queue_id = pool->queue_id;
> > +
> > + err = pool->netdev->netdev_ops->ndo_bpf(pool->netdev, &bpf);
> > +
> > + if (err)
> > + WARN(1, "Failed to disable zero-copy!\n");
> > + }
> > +}
> > +
> > int xp_assign_dev(struct xsk_buff_pool *pool, struct net_device *netdev,
> > u16 queue_id, u16 flags)
> > {
> > @@ -122,6 +141,8 @@ int xp_assign_dev(struct xsk_buff_pool *pool, struct net_device *netdev,
> > if (xsk_get_pool_from_qid(netdev, queue_id))
> > return -EBUSY;
> >
> > + pool->netdev = netdev;
> > + pool->queue_id = queue_id;
> > err = xsk_reg_pool_at_qid(netdev, pool, queue_id);
> > if (err)
> > return err;
> > @@ -155,11 +176,15 @@ int xp_assign_dev(struct xsk_buff_pool *pool, struct net_device *netdev,
> > if (err)
> > goto err_unreg_pool;
> >
> > - pool->netdev = netdev;
> > - pool->queue_id = queue_id;
> > + if (!pool->dma_pages) {
> > + WARN(1, "Driver did not DMA map zero-copy buffers");
> > + goto err_unreg_xsk;
> > + }
> > pool->umem->zc = true;
> > return 0;
> >
> > +err_unreg_xsk:
> > + xp_disable_drv_zc(pool);
> > err_unreg_pool:
> > if (!force_zc)
> > err = 0; /* fallback to copy mode */
> > @@ -170,25 +195,10 @@ int xp_assign_dev(struct xsk_buff_pool *pool, struct net_device *netdev,
> >
> > void xp_clear_dev(struct xsk_buff_pool *pool)
> > {
> > - struct netdev_bpf bpf;
> > - int err;
> > -
> > - ASSERT_RTNL();
> > -
> > if (!pool->netdev)
> > return;
> >
> > - if (pool->umem->zc) {
> > - bpf.command = XDP_SETUP_XSK_POOL;
> > - bpf.xsk.pool = NULL;
> > - bpf.xsk.queue_id = pool->queue_id;
> > -
> > - err = pool->netdev->netdev_ops->ndo_bpf(pool->netdev, &bpf);
> > -
> > - if (err)
> > - WARN(1, "Failed to disable zero-copy!\n");
> > - }
> > -
> > + xp_disable_drv_zc(pool);
> > xsk_clear_pool_at_qid(pool->netdev, pool->queue_id);
> > dev_put(pool->netdev);
> > pool->netdev = NULL;
> > @@ -233,14 +243,61 @@ void xp_put_pool(struct xsk_buff_pool *pool)
> > }
> > }
> >
> > +static struct xsk_dma_map *xp_find_dma_map(struct xsk_buff_pool *pool)
> > +{
> > + struct xsk_dma_map *dma_map;
> > +
> > + list_for_each_entry(dma_map, &pool->umem->xsk_dma_list, list) {
> > + if (dma_map->dev == pool->netdev)
> > + return dma_map;
> > + }
> > +
> > + return NULL;
> > +}
> > +
> > +static void xp_destroy_dma_map(struct xsk_dma_map *dma_map)
> > +{
> > + list_del(&dma_map->list);
> > + kfree(dma_map);
> > +}
> > +
> > +static void xp_put_dma_map(struct xsk_dma_map *dma_map)
> > +{
> > + if (!refcount_dec_and_test(&dma_map->users))
> > + return;
> > +
> > + xp_destroy_dma_map(dma_map);
> > +}
> > +
> > +static struct xsk_dma_map *xp_create_dma_map(struct xsk_buff_pool *pool)
> > +{
> > + struct xsk_dma_map *dma_map;
> > +
> > + dma_map = kzalloc(sizeof(*dma_map), GFP_KERNEL);
> > + if (!dma_map)
> > + return NULL;
> > +
> > + dma_map->dev = pool->netdev;
> > + refcount_set(&dma_map->users, 1);
> > + list_add(&dma_map->list, &pool->umem->xsk_dma_list);
> > + return dma_map;
> > +}
> > +
> > void xp_dma_unmap(struct xsk_buff_pool *pool, unsigned long attrs)
> > {
> > + struct xsk_dma_map *dma_map;
> > dma_addr_t *dma;
> > u32 i;
> >
> > if (pool->dma_pages_cnt == 0)
> > return;
> >
> > + dma_map = xp_find_dma_map(pool);
> > + if (!dma_map) {
> > + WARN(1, "Could not find dma_map for device");
> > + return;
> > + }
> > +
> > for (i = 0; i < pool->dma_pages_cnt; i++) {
> > dma = &pool->dma_pages[i];
> > if (*dma) {
> > @@ -250,6 +307,7 @@ void xp_dma_unmap(struct xsk_buff_pool *pool, unsigned long attrs)
> > }
> > }
> >
> > + xp_put_dma_map(dma_map);
>
> I believe that the logic in this function is not correct. Basically, the
> driver calls xp_dma_[un]map when a socket is enabled/disabled on a given
> queue of a given netdev. On xp_dma_map, if the UMEM is already mapped
> for that netdev, we skip all the logic, but on xp_dma_unmap you unmap
> the pages unconditionally, only after that you check the refcount. This
> is not symmetric, and the pages will be unmapped when the first socket
> is closed, rendering the rest of sockets unusable.
Thanks for spotting this. Will fix.
/Magnus
> > kvfree(pool->dma_pages);
> > pool->dma_pages_cnt = 0;
> > pool->dev = NULL;
> > @@ -271,14 +329,29 @@ static void xp_check_dma_contiguity(struct xsk_buff_pool *pool)
> > int xp_dma_map(struct xsk_buff_pool *pool, struct device *dev,
> > unsigned long attrs, struct page **pages, u32 nr_pages)
> > {
> > + struct xsk_dma_map *dma_map;
> > dma_addr_t dma;
> > u32 i;
> >
> > + dma_map = xp_find_dma_map(pool);
> > + if (dma_map) {
> > + pool->dma_pages = dma_map->dma_pages;
> > + refcount_inc(&dma_map->users);
> > + return 0;
> > + }
> > +
> > + dma_map = xp_create_dma_map(pool);
> > + if (!dma_map)
> > + return -ENOMEM;
> > +
> > pool->dma_pages = kvcalloc(nr_pages, sizeof(*pool->dma_pages),
> > GFP_KERNEL);
> > - if (!pool->dma_pages)
> > + if (!pool->dma_pages) {
> > + xp_destroy_dma_map(dma_map);
> > return -ENOMEM;
> > + }
> >
> > + dma_map->dma_pages = pool->dma_pages;
> > pool->dev = dev;
> > pool->dma_pages_cnt = nr_pages;
> > pool->dma_need_sync = false;
> > @@ -288,6 +361,7 @@ int xp_dma_map(struct xsk_buff_pool *pool, struct device *dev,
> > DMA_BIDIRECTIONAL, attrs);
> > if (dma_mapping_error(dev, dma)) {
> > xp_dma_unmap(pool, attrs);
> > + xp_destroy_dma_map(dma_map);
> > return -ENOMEM;
> > }
> > if (dma_need_sync(dev, dma))
> >
>
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